Articles of controllably bonded sheets and methods for making same

ABSTRACT

Described herein are articles and methods of making articles, including a first sheet and a second sheet, wherein the thin sheet and carrier are bonded together using a coating layer, preferably a hydrocarbon polymer coating layer, and associated deposition methods and inert gas treatments that may be applied on either sheet, or both, to control van der Waals, hydrogen and covalent bonding between the sheets. The coating layer bonds the sheets together to prevent formation of a permanent bond at high temperature processing while at the same time maintaining a sufficient bond to prevent delamination during high temperature processing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 371 ofInternational Application No. PCT/US2017/049025, filed on Aug. 29, 2017,which claims the benefit of priority under 35 U.S.C. § 119 of U.S.Provisional Application No. 62/381,731 filed on Aug. 31, 2016, thecontent of which is relied upon and incorporated herein by reference inits entirety.

FIELD

The present disclosure relates generally to articles including andmethods for making sheets on carriers and, more particularly, toarticles including and methods for making flexible glass sheetscontrollably bonded on glass carriers.

BACKGROUND

Flexible substrate materials offer the ability to manufacture cheaperdevices using roll-to-roll processing, and the potential to makethinner, lighter, more flexible and durable displays. However, thetechnology, equipment, and processes required for roll-to-rollprocessing of high quality displays are not yet fully developed. Becausepanel makers have already heavily invested in toolsets to process largesheets of glass, laminating a flexible substrate to a carrier and makingdisplay devices on the flexible substrate by sheet-to-sheet processingoffers a shorter term solution to develop the value proposition ofthinner, lighter, and more flexible displays. Displays have beendemonstrated on polymer sheets, for example polyethylene naphthalate(PEN), where the device fabrication was sheet-to-sheet with the PENlaminated to a glass carrier. However, the upper temperature limit ofthe PEN limits the device quality and process that can be used. Inaddition, the high permeability of the polymer substrate leads toenvironmental degradation of organic light emitting diode (OLED) deviceswhere a near hermetic package is required. Thin film encapsulationoffers the promise to overcome this limitation, but it has not yet beendemonstrated to offer acceptable yields at large volumes.

In a similar manner, display devices can be manufactured using a glasscarrier laminated to one or more thin glass substrates. It isanticipated that the low permeability and improved temperature andchemical resistance of the thin glass will enable higher performancelonger lifetime flexible displays.

In low temperature polysilicon (LTPS) device fabrication processes, forexample with temperatures typically approaching 600° C. or greater,vacuum, and wet etch environments may also be used. These conditionslimit the materials that may be used, and place high demands on thecarrier/thin sheet. Accordingly, what is desired is a carrier approachthat utilizes the existing capital infrastructure of the manufacturers,enables processing of thin glass, i.e., glass having a thickness ≤0.3millimeters (mm) thick, without contamination or loss of bond strengthbetween the thin glass and carrier at higher processing temperatures,and wherein the thin glass debonds easily from the carrier at the end ofthe process.

One commercial advantage is that manufacturers will be able to utilizetheir existing capital investment in processing equipment while gainingthe advantages of the thin glass sheets for photo-voltaic (PV)structures, OLED, liquid crystal displays (LCDs) and patterned thin filmtransistor (TFT) electronics, for example. Additionally, such anapproach enables process flexibility, including: processes for cleaningand surface preparation of the thin glass sheet and carrier tofacilitate bonding.

A challenge of known bonding methods is the high temperature used toprocess polysilicon TFTs. The demand for higher pixel density, highresolution, and fast refresh rates on hand held displays, notebook anddesktop displays, as well as the wider use of OLED displays, is pushingpanel makers from amorphous silicon TFT backplanes to oxide TFT orpolysilicon TFT backplanes. Because OLEDs are a current driven device,high mobility is desired. Polysilicon TFTs also offer the advantage ofintegration of drivers and other components activation. In polysiliconTFT processes, higher temperature is preferred for dopant activation,ideally at temperature over 600° C.

SUMMARY

In light of the above, there is a need for a thin sheet-carrier articlethat can withstand the rigors of TFT and flat panel display (FPD)processing, including high temperature processing (without outgassingthat would be incompatible with the semiconductor or display makingprocesses in which it will be used), yet allow the entire area of thethin sheet to be removed (either all at once, or in sections) from thecarrier so as to allow reuse of the carrier for processing another thinsheet. The present specification describes methods to control adhesionbetween the multi-sheet articles (e.g., carrier and thin sheet) andcreate a temporary bond sufficiently strong to survive TFT and FPDprocessing (including processing at temperatures of about 300° C., about400° C., about 500° C., and up to at least 600° C., including any rangesand subranges therebetween) but weak enough to permit debonding of thesheet from the carrier, even after high-temperature processing. Suchcontrolled bonding can be utilized to create an article having are-usable carrier, or alternately an article having patterned areas ofcontrolled bonding between a carrier and a sheet. More specifically, thepresent disclosure provides coating layers (including various materialsand associated surface treatments), that may be provided on the thinsheet, the carrier, or both, to control both room-temperature van derWaals, and/or hydrogen, bonding and high temperature covalent bondingbetween the thin sheet and carrier. Even more specifically, the presentdisclosure describes methods of depositing a coating layer that can bonda thin sheet to a carrier, methods for preparing the coating layer forbonding, and bonding the coating layer to both the thin sheet and thecarrier. These methods produce bonding between the components such thatthe bonding energy is not too high, which might render the componentsinseparable after electronic device processing, and such that thebonding energy is not too low, which might lead to compromised bondingquality thus leading to possible debonding or fluid ingress between thethin sheet and carrier during electronic device processing. Thesemethods also produce a glass article that exhibits low outgassing andsurvives high temperature processing for example, LTPS TFT processing aswell as additional processing steps, for example wet cleaning and dryetching. In alternative examples, the coating layers may be used tocreate various controlled bonding areas (wherein the carrier and thinsheet remain sufficiently bonded through various processes, includingvacuum processing, wet processing, and/or ultrasonic cleaningprocessing), together with covalent bonding regions to provide forfurther processing options, for example, maintaining hermeticity betweenthe carrier and sheet even after dicing the article into smaller piecesfor additional device processing.

In a first aspect, there is an article comprising:

-   -   a first sheet comprising a first sheet bonding surface, and    -   a coating layer comprising a first coating layer bonding surface        and a second coating layer bonding surface, the coating layer        comprising a polymerized hydrogenated amorphous hydrocarbon        compound, the coating layer has a refractive index above about        1.8.

In some examples of aspect 1, the coating layer has a refractive indexless than about 2.5.

In another example of aspect 1, the coating layer has a refractive indexbetween about 1.9 and about 2.4.

In a second aspect, there is an article comprising:

-   -   a first sheet comprising a first sheet bonding surface, and    -   a coating layer comprising a first coating layer bonding surface        and a second coating layer bonding surface, the coating layer        comprising a polymerized hydrogenated amorphous hydrocarbon        compound, the coating layer has an optical band gap of less than        2 eV.

In some examples of aspect 2, the coating layer has an optical band gapranging from about 0.8 to about 2 eV.

In another example of aspect 2, the coating layer has an optical bandgap ranging from about 1.2 to about 1.8 eV.

In a third aspect, there is an article comprising:

-   -   a first sheet comprising a first sheet bonding surface, and    -   a coating layer comprising a first coating layer bonding surface        and a second coating layer bonding surface, the coating layer        comprising a polymerized hydrogenated amorphous hydrocarbon        compound, the coating layer has a Raman spectrum with an        intensity ratio (D/G ratio) of a peak (D band) appearing in the        range of 1350 to 1400 cm⁻¹ to a peak (G band) appearing in the        range of 1530 to 1600 cm⁻¹ of about 0.5 to about 0.6.

In some examples of aspect 3, the intensity ratio (D/G ratio) may be inthe range of about 0.52 to about 0.58.

In another example of aspect 3, the peak (D band) may be at about 1380cm⁻¹ and the peak (G band) may be at about 1530 cm⁻¹ of Raman spectrum.

In a fourth aspect, there is an article comprising:

-   -   a first sheet comprising a first sheet bonding surface;    -   a coating layer comprising a first coating layer bonding surface        and a second coating layer bonding surface, the coating layer        comprising a polymerized hydrogenated amorphous hydrocarbon        compound, the coating layer being formed by depositing a        precursor compound having a hydrogen and carbon content of        greater than 90 weight percent; and    -   the first coating layer bonding surface being bonded with the        first sheet bonding surface with a bond energy of less than 700        mJ/m² after holding the article in a furnace at a temperature of        600° C. for 10 minutes in a nitrogen atmosphere.

In a fifth aspect, there is provided an article of any of aspects 1-4,the coating layer is formed by depositing a hydrocarbon compound, thehydrocarbon compound having a formula of C_(n)H_(y), wherein n is 1 to 6and y is 2 to 14.

In some examples of aspect 5, the first coating layer bonding surfacehaving an as-deposited surface energy greater than about 50 mJ/m².

In mother example of aspect 5, the as-deposited surface energy of thefirst coating layer bonding surface being less than about 60 mJ/m².

In mother example of aspect 5, the as-deposited surface energy of thefirst coating layer bonding surface being between about 50 mJ/m² andabout 58 mJ/m².

In another example of aspect 5, the hydrocarbon compound is an alkane,the alkane being selected from the group consisting of methane, ethane,propane, butane, pentane and hexane.

In another example of aspect 5, the hydrocarbon compound is an alkene,the alkene being selected from the group consisting of ethylene,propylene, butylene, pentene and hexene.

In another example of aspect 5, the hydrocarbon compound is an alkyne,the alkyne being selected from the group consisting of ethyne, propyne,butyne, pentyne and hexyne.

In a sixth aspect, there is provided an article of any of aspects 1-5,further comprising a second sheet comprising a second sheet bondingsurface.

In some examples of aspect 6, the second coating layer bonding surfacebeing bonded with the second sheet bonding surface.

In another example of aspect 6, the first sheet being a glass sheet.

In another example of aspect 6, the second sheet being a glass sheet.

In another example of aspect 6, the first sheet being a glass sheet andthe second sheet being a glass sheet.

In a seventh aspect, there is provided an article of any of the examplesof aspect 6, the polymerized hydrocarbon compound being formed bydepositing the hydrocarbon compound on either the first sheet bondingsurface or the second sheet bonding surface using low-pressure plasmachemical vapor deposition or atmospheric pressure plasma chemical vapordeposition.

In a eighth aspect, there is provided an article of any of aspects 1-6,the coating layer having an average thickness of less than 10 nm.

In a ninth aspect, there is provided an article of any of aspects 1-6,the coating layer having an average thickness of less than 5 nm.

In a tenth aspect, there is provided an article of any of aspects 1-6,the coating layer being a single layer.

In an eleventh aspect, there is provided an article of any of aspects1-6, the first sheet having an average thickness greater than or equalto 200 μm.

In a twelfth aspect, there is provided an article of any of aspects 1-6,the first coating layer bonding surface being bonded with the firstsheet bonding surface with a bond energy of less than 600 mJ/m² afterholding the article in a furnace at a temperature of 600° C. for 10minutes in a nitrogen atmosphere.

In a thirteenth aspect, there is provided an article of any of aspects1-6, the first coating layer bonding surface being bonded with the firstsheet bonding surface with a bond energy of less than 500 mJ/m² afterholding the article in a furnace at a temperature of 500° C. for 10minutes in a nitrogen atmosphere.

In a fourteenth aspect, there is provided an article of any of theExamples of aspect 6, the change in percent bubble area of the coatinglayer being less than 10 percent according to Outgassing Test #1 afterholding the article in a furnace at a temperature of 600° C. for 10minutes in a nitrogen atmosphere.

In a fifteenth aspect, there is provided an article of any of aspects1-6, the change in percent bubble area of the coating layer being lessthan 10 percent according to Outgassing Test #1 after holding thearticle in a furnace at a temperature of 500° C. for 10 minutes in anitrogen atmosphere.

In a sixteenth aspect, there is provided an article of any of aspects1-6, the change in percent bubble area of the coating layer being lessthan 5 percent according to Outgassing Test #1 after holding the articlein a furnace at a temperature of 500° C. for 10 minutes in a nitrogenatmosphere.

In a seventeenth aspect, there is provided an article of any of aspects12-16, the first coating layer bonding surface being exposed to anitrogen and oxygen atmosphere to increase the surface energy of thefirst coating layer bonding surface prior to holding the article in afurnace at a temperature of 500° C. or greater for 10 minutes in anitrogen atmosphere.

In an eighteenth aspect, there is a method of making an articlecomprising:

-   -   forming a coating layer comprising a polymerized hydrocarbon        compound on a bonding surface of a first sheet by depositing a        hydrocarbon compound on the bonding surface of the first sheet        using plasma chemical vapor deposition, the coating layer        comprising a first coating layer bonding surface bonded to the        bonding surface of the first sheet and a second coating layer        bonding surface, and the hydrocarbon compound having a formula        of C_(n)H_(y), wherein n is 1 to 6 and y is 2 to 14; and    -   bonding the second coating layer bonding surface with a second        sheet bonding surface of a second sheet, the second coating        layer bonding surface being bonded with the second sheet bonding        surface with a bond energy of less than 700 mJ/m² after holding        the article in a furnace at a temperature of 600° C. for 10        minutes in a nitrogen atmosphere.

In some examples of aspect 18, the hydrocarbon compound is an alkane,the alkane being selected from the group consisting of methane, ethane,propane, butane, pentane and hexane.

In another example of aspect 18, the hydrocarbon compound is an alkene,the alkene being selected from the group consisting of ethylene,propylene, butylene, pentene and hexene.

In another example of aspect 18, the hydrocarbon compound is an alkyne,the alkyne being selected from the group consisting of ethyne, propyne,butyne, pentyne and hexyne.

In another example of aspect 18, the polymerized hydrocarbon compoundbeing a hydrogenated amorphous compound.

In another example of aspect 18, the first sheet being a glass sheet.

In another example of aspect 18, the second sheet being a glass sheet.

In another example of aspect 18, the first sheet being a glass sheet andthe second sheet being a glass sheet.

In nineteenth aspect, there is provided an article of aspect 18, furthercomprising increasing the surface energy of the second coating layerbonding surface before the second sheet bonding surface is bonded to thesecond coating layer bonding surface, wherein the surface energy isincreased by exposing the second coating layer bonding surface tooxygen, nitrogen, or a combination thereof.

In another example of aspect 19, the coating layer having an averagethickness of less than 10 nm.

In another example of aspect 19, the coating layer having an averagethickness of less than 5 nm.

In another example of aspect 19, the second sheet having an averagethickness less than or equal to 300 μm.

In another example of aspect 19, the plasma chemical vapor depositionbeing low-pressure plasma chemical vapor deposition or atmosphericpressure plasma chemical vapor deposition.

In a twentieth aspect, there is provided an article of aspect 19, thesecond coating layer bonding surface being bonded with the second sheetbonding surface with a bond energy of less than 600 mJ/m² after holdingthe article in a furnace at a temperature of 500° C. for 10 minutes in anitrogen atmosphere.

In a twenty-first aspect, there is provided an article of aspect 19, thechange in percent bubble area of the second coating layer being lessthan 10 percent according to Outgassing Test #1 after holding thearticle in a furnace at a temperature of 600° C. for 10 minutes in anitrogen atmosphere.

In a twenty-second aspect, there is provided an article of aspect 19,the change in percent bubble area of the second coating layer being lessthan 10 percent according to Outgassing Test #1 after holding thearticle in a furnace at a temperature of 500° C. for 10 minutes in anitrogen atmosphere.

In a twenty-third aspect, there is provided an article of aspect 19, thechange in percent bubble area of the second coating layer being lessthan 5 percent according to Outgassing Test #1 after holding the articlein a furnace at a temperature of 500° C. for 10 minutes in a nitrogenatmosphere.

In a twenty-fourth aspect, there is provided an article of aspect 18,the second coating layer bonding surface having an as-deposited surfaceenergy greater than about 50 mJ/m².

In a twenty-fifth aspect, there is provided an article of any of aspects18-23, the coating layer having a refractive index above about 1.8 or 2.

In a twenty-sixth aspect, there is provided an article of any of aspects18-23, the coating layer having an optical band gap less than about 2eV.

In a twenty-seventh aspect, there is provided an article of any ofaspects 18-23, the coating layer having an intensity ratio (D/G ratio)of a peak (D band) appearing in the range of 1350 to 1400 cm⁻¹ to a peak(G band) appearing in the range of 1530 to 1600 cm⁻¹ of Raman spectrumin the range of about 0.5 to about 0.6.

Any one of the above aspects (or examples of those aspects) may beprovided alone or in combination with any one or more of the examples ofthat aspect discussed above; e.g., the first aspect may be providedalone or in combination with any one or more of the examples of thefirst aspect discussed above; and the second aspect may be providedalone or in combination with any one or more of the examples of thesecond aspect discussed above; and so-forth.

The accompanying drawings are included to provide a furtherunderstanding of principles of the disclosure, and are incorporated inand constitute a part of this specification. The drawings illustratesome examples(s), and together with the description serve to explain, byway of example, principles and operation thereof. It is to be understoodthat various features disclosed in this specification and in thedrawings can be used in any and all combinations. By way of non-limitingexample the various features may be combined with one another as setforth in the specification, above, as aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features, examples and advantages of aspects of theexamples disclosed in the present specification are better understoodwhen the following detailed description thereof is read with referenceto the accompanying drawings, in which:

FIG. 1 is a schematic side view of an article having a carrier bonded toa thin sheet with a coating layer therebetween.

FIG. 2 is an exploded and partially cut-away view of the article in FIG.1 .

FIG. 3 is a graph of the bond energy and change in percent bubble areafor thin glass bonded to a carrier with a hydrogenated amorphousplasma-polymerized hydrocarbon coating layer formed by a methaneprecursor.

FIG. 4 is a graph of the surface energy before and after surfaceactivation for a hydrogenated amorphous plasma-polymerized hydrocarboncoating layer formed by an ethylene precursor.

FIG. 5 is a graph of the bond energy and change in percent bubble areafor thin glass bonded to a carrier with a hydrogenated amorphousplasma-polymerized hydrocarbon coating layer formed by an ethyleneprecursor.

FIG. 6 is a graph of the bond energy and change in percent bubble areafor thin glass bonded to a carrier with a hydrogenated amorphousplasma-polymerized hydrocarbon coating layer formed by an ethyleneprecursor.

FIG. 7 is a graph of the surface energy for a prior art coating layerformed by a methane precursor.

FIG. 8 is a graph of Raman characterization of a hydrogenated amorphousplasma-polymerized hydrocarbon coating layer formed by an ethyleneprecursor.

DETAILED DESCRIPTION

Examples will now be described more fully hereinafter with reference tothe accompanying drawings. Whenever possible, the same referencenumerals are used throughout the drawings to refer to the same or likeparts. However, the claimed subject matter may be embodied in manydifferent forms and should not be construed as limited to the examplesset forth herein.

Directional terms as used herein (e.g., up, down, right left, front,back, top, bottom) are made only with reference to the figures as drawnand are not intended to imply absolute orientation.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another embodiment includes from the one particular valueand/or to the other particular value. Similarly, when values areexpressed as approximations, by use of the antecedent “about,” it willbe understood that the particular value forms another embodiment. Itwill be further understood that the endpoints of each of the ranges aresignificant both in relation to the other endpoint, and independently ofthe other endpoint.

Provided are solutions for the processing of a second sheet on a firstsheet, whereby at least portions (including up to all) of a secondsheet, for example, a thin sheet (for example a thin glass sheet),remain “non-bonded” so that devices processed on the thin sheet may beremoved from the first sheet, for example, a carrier, for example aglass carrier. In order to maintain advantageous surface shapecharacteristics, the carrier is typically a display grade glasssubstrate. Accordingly, in some situations, it is wasteful and expensiveto merely dispose of the carrier after one use. Thus, in order to reducecosts of display manufacture, it is desirable to be able to reuse thecarrier to process more than one thin sheet substrate. The presentdisclosure sets forth articles and methods for enabling a thin sheet tobe processed through the harsh environment of the processing lines, forexample TFT, including high temperature processing, wherein hightemperature processing is processing at a temperature ≥400° C., and mayvary depending upon the type of device being made, for example,temperatures up to about 450° C. as in amorphous silicon or amorphousindium gallium zinc oxide (IGZO) backplane processing, up to about500-550° C. as in crystalline IGZO processing, or up to about 600-650°C. as is typical in LTPS and TFT processes—and yet still allows the thinsheet to be easily removed from the carrier without damage (for example,wherein one of the carrier and the thin sheet breaks or cracks into twoor more pieces) to the thin sheet or carrier, whereby the carrier may bereused.

Glass Article

As shown in FIGS. 1 and 2 , an article 2, for example a glass article,has a thickness 8, and includes a first sheet 10 (for example a carrier)having a thickness 18, a second sheet 20 (e.g., a thin glass sheet)having a thickness 28, and a coating layer 30 having a thickness 38.Thickness 28 of the second sheet 20 may be, for example, equal to orless than about 300 micrometers (μm, or microns), including but notlimited to thicknesses of, for example, about 10 to about 50micrometers, about 50 to about 100 micrometers, about 100 to about 150μm, about 150 to about 300 μm, about 300 μm, about 250 μm, about 200 μm,about 190 μm, about 180 μm, about 170 μm, about 160 μm, about 150 μm,about 140 μm, about 130 μm, about 120 μm, about 110 μm, about 100 μm,about 90 μm, about 80 μm, about 70 μm, about 60 μm, about 50 μm, about40 μm, about 30 μm, about 20 μm, or about 10 μm, including any rangesand subranges therebetween.

The glass article 2 is arranged to allow the processing of second sheet20 in equipment designed for thicker sheets, for example, those on theorder of greater than or equal to about 0.4 mm, for example 0.4 mm, 0.5mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, or 1.0 mm, although the second sheet20 itself is equal to or less than about 300 μm. The thickness 8, whichis the sum of thicknesses 18, 28, and 38, can be equivalent to that ofthe thicker sheet for which a piece of equipment, for example, equipmentdesigned to dispose electronic device components onto substrate sheets,was designed to process. In some examples, if the processing equipmentwas designed for a 700 μm sheet, and the second sheet had a thickness 28of 300 μm, then thickness 18 would be selected as 400 μm, assuming thatthickness 38 is negligible. That is, the coating layer 30 is not shownto scale, but rather it is greatly exaggerated for sake of illustrationonly. Additionally, in FIG. 2 , the coating layer is shown in cut-away.The coating layer can be disposed uniformly over the bonding surface 14when providing a reusable carrier. Typically, thickness 38 will be onthe order of nanometers, for example 2 nm to 250 nm, 5 nm to 100 nm, 8nm to 80 nm, or 10 to 50 nm, or about 20, 30, or 40 nm. The presence ofa coating layer may be detected by surface chemistry analysis, forexample by time-of-flight secondary ion mass spectrometry (ToF SIMS).

First sheet 10, which may be used as a carrier for example, has a firstsurface 12, a bonding surface 14, and a perimeter 16. The first sheet 10may be of any suitable material including glass. The first sheet can bea non-glass material, for example, ceramic, glass-ceramic, silicon, ormetal (as the surface energy and/or bonding may be controlled in amanner similar to that described below in connection with a glasscarrier). If made of glass, first sheet 10 may be of any suitablecomposition including alumino-silicate, boro-silicate,alumino-boro-silicate, soda-lime-silicate, and may be either alkalicontaining or alkali-free depending upon its ultimate application.Further, in some examples, when made of glass, glass-ceramic, or othermaterial, the first sheet bonding surface can be made of a coating orlayer of metal material disposed on the underlying bulk material of thefirst sheet. Thickness 18 may be from about 0.2 to about 3 mm, orgreater, for example, about 0.2 mm, about 0.3 mm, about 0.4 mm, about0.5 mm, about 0.6 mm, about 0.65 mm, about 0.7 mm, about 1.0 mm, about2.0 mm, or about 3.0 mm, or greater, including any ranges and subrangestherebetween, and will depend upon the thickness 28, and thickness 38when thickness 38 is non-negligible, as noted above. The thickness 18 ofthe first sheet 10 in some examples may be greater than the thickness 28of the second sheet 20. In some examples, thickness 18 may be less thanthickness 28. In one embodiment, the first sheet 10 may be made of onelayer, as shown, or multiple layers (including multiple thin sheets)that are bonded together. Further, the first sheet may be of a Gen 1size or larger, for example, Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 or larger(e.g., sheet sizes from about 100 mm×100 mm to about 3 meters×3 metersor greater).

The second sheet 20 has a first surface 22, a bonding surface 24, and aperimeter 26. Perimeters 16 (first sheet 10) and 26 (second sheet 20)may be of any suitable shape, may be the same as one another, or may bedifferent from one another. Further, the second sheet 20 may be of anysuitable material including glass, ceramic, glass-ceramic, silicon, ormetal. As described above for the first sheet 10, when made of glass,second sheet 20 may be of any suitable composition, includingalumino-silicate, boro-silicate, alumino-boro-silicate,soda-lime-silicate, and may be either alkali containing or alkali-freedepending upon its ultimate application. The coefficient of thermalexpansion of the thin sheet can be matched substantially the same withthat of the first sheet to reduce any warping of the article duringprocessing at elevated temperatures. The thickness 28 of the secondsheet 20 is about 300 μm or less, such as about 200 μm or about 100 μm,or thicknesses as noted above. Further, the second sheet 20 may be of aGen 1 size or larger, for example, Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 orlarger (e.g., sheet sizes from about 100 mm×100 mm to about 3 meters×3meters or greater).

The glass article 2 can have a thickness that accommodates processingwith existing equipment, and likewise it can survive the harshenvironment in which the processing takes place. For example, flat paneldisplay (FPD) processing may include wet ultrasonic, vacuum, and hightemperature (e.g., ≥400° C., ≥450° C., ≥500° C., ≥550° C., and up to atleast 600° C.), processing, including any ranges and subrangestherebetween.

To survive the harsh environment in which article 2 will be processed,the bonding surface 14 should be bonded to bonding surface 24 withsufficient strength so that the second sheet 20 does not separate fromfirst sheet 10. This strength should be maintained throughout theprocessing so that second sheet 20 does not separate from first sheet 10during processing. Further, to allow second sheet 20 to be removed fromfirst sheet 10 (so that a first sheet 10, for example a carrier, may bereused, for example), the bonding surface 14 should not be bonded tobonding surface 24 too strongly either by the initially designed bondingforce, and/or by a bonding force that results from a modification of theinitially designed bonding force as may occur, for example, when thearticle undergoes processing at high temperatures, e.g., temperatures of≥ about 400° C. to about 500° C., ≥ about 500° C., to about 600° C., andat least 600° C., including any ranges and subranges therebetween. Thecoating layer 30 may be used to control the strength of bonding betweenbonding surface 14 and bonding surface 24 so as to achieve both of theseobjectives. The controlled bonding force is achieved by controlling thecontributions of van der Waals (and/or hydrogen bonding) and covalentattractive energies to the total adhesion energy which is controlled bymodulating the polar and non-polar surface energy components of firstsheet 10 and second sheet 20. Alternatively, the coating layer 30 maycompletely cover one bonding surface (for example bonding surface 14) ofone sheet and present a coating layer bonding surface (havingcharacteristics independent of those on the one bonding surface) forcoupling to another bonding surface (for example bonding surface 24) ofanother sheet. This controlled bonding is strong enough to survive FPDprocessing, for instance, including temperatures ≥400° C., and in someinstances, processing temperatures of ≥500° C., ≥550° C., and up to atleast 600° C., including any ranges and subranges therebetween, andremain debondable by application of a force sufficient to separate thesheets but not cause significant damage to first sheet 10 and/or secondsheet 20. For example, the applied force should not break either thefirst sheet 10 or second sheet 20. Such debonding permits removal ofsecond sheet 20 and the devices fabricated thereon, and also allows forre-use of first sheet 10 as a carrier.

Although the coating layer 30 is shown as a solid layer between sheet 20and sheet 10, such need not be the case. For example, the layer 30 maybe on the order of about 0.1 nm to about 1 μm thick (e.g., about 1 nm toabout 10 nm, about 10 nm to about 50 nm, about 50 nm to about 100 nm,about 250 nm, about 500 nm to about 1 μm), and may not completely coverthe entire portion of the bonding surface 14. For example, the coverageon bonding surface 14 may be ≤ about 100%, from about 1% to about 100%,from about 10% to about 100%, from about 20% to about 90%, or from about50% to about 90% of the bonding surface 14, including any ranges andsubranges therebetween. In other examples, the layer 30 may be up toabout 50 nm thick, or in other examples even up to about 100 nm to about250 nm thick. The coating layer 30 may be considered to be disposedbetween sheet 10 and sheet 20 even though it may not contact one or theother of sheet 10 and sheet 20. In other examples, the coating layer 30modifies the ability of the bonding surface 14 to bond with bondingsurface 24, thereby controlling the strength of the bond between thesheet 10 and sheet 20. The material and thickness of the coating layer30, as well as the treatment of the bonding surfaces 14, 24 prior tobonding, can be used to control the strength of the bond (energy ofadhesion) between sheet 10 and sheet 20.

Coating Layer Composition

Examples of coating layers include hydrocarbon polymers. Preferably, thehydrocarbon polymers are hydrogenated amorphous hydrocarbon polymers.Such hydrocarbon polymers may be formed by depositing a hydrocarbonprecursor compound on either the first sheet (for example a carrier) orthe second sheet (for example a thin sheet).

One group of hydrocarbon precursor compounds are compounds of formulaC_(n)H_(y), wherein n is 1 to 6 and y is 2 to 14. In some examples, n is1 to 4 and y is 2 to 10. The hydrocarbon compounds can be linear orbranched. In some examples, the coating layer formed by depositing ahydrocarbon precursor compound has a combined carbon and hydrogencontent of at least 80 weight percent, at least 85 weight percent, atleast 90 weight percent, or at least 95 weight percent. In someexamples, the precursor compound is deposited to form the coating layerhas a combined carbon and hydrogen content of at least 80 weightpercent, at least 85 weight percent, at least 90 weight percent, atleast 95 weight percent, at least 98 weight percent, at least 99 weightpercent, or greater than 99.5 weight percent.

Examples of hydrocarbon precursor compounds include alkanes. An alkanecan include methane, ethane, propane, butane, pentane and hexane. Insome examples, the hydrocarbon precursor compounds include at least onecarbon-carbon double bond, for example, an alkene. An alkene can includeethylene, propylene, butylene, pentene and hexane. The carbon-carbondouble bond in the alkene can be present at various positions in thecompound, for instance, but-1-ene or but-2-ene. In yet other examples,the hydrocarbon precursor compounds includes at least one carbon-carbontriple bond, for example, an alkyne. An alkyne can include ethyne,propyne, butyne, pentyne and hexyne. In some examples, the carbon-carbontriple bond in the alkyne is present at various positions in thecompound, for instance, 1-butyne or 2-butyne.

The coating layer can comprise a single layer. The coating layerpreferably has a thickness of less than 50 nm, for example less thanabout 40 nm, less than about 30 nm, less than about 20 nm, less thanabout 15 nm, less than about 12 nm, less than about 10 nm, less thanabout 8 nm, less than about 5 nm.

The coating layer is preferably a hydrogenated amorphousplasma-polymerized hydrocarbon compound having certain properties.Optical properties of the coating were obtained from spectroscopicellipsometry data, by the Tauc-Lorentz model (J. Tauc, R Grigorovici, A.Vancu, “Optical properties and electronic structure of amorphousgermanium,” Phys. Status Solidi B, 15 (1966)). In some examples, thecoating layer has a refractive index in the range of about 1.8 to about2.5, for example in a range of about 1.9 to about 2.4, or equal to orgreater than about 2, or equal to or greater than about 2.1, or equal toor greater than about 2.2, or equal to or greater than about 2.3. Therefractive index of hydrogenated amorphous plasma-polymerizedhydrocarbon coating layers on carrier sheets was determined using aWollam variable angle spectroscopic ellipsometer. The refractive indexwas determined at 20° C. for light having a wavelength of 632 nm. Inanother embodiment, the coating layer may have one or moreoptoelectronic properties. These optoelectronic properties may resultfrom a small band gap ranging from about 0.8 eV to less than about 2 eV,for example ranging from about 1.2 eV to about 1.8 eV or about 1.4 eV toabout 1.6 eV. Optoelectronic properties may, for example, include theabsorption, transmission, or emission of light.

In some examples, the coating layer is characterized by Ramanspectroscopy. In amorphous diamond-like carbon thin films Ramanspectroscopy is a preferred method for determining film characteristics,for example, Raman spectra of the films show two distinct peaks. TheRaman spectrum can include a G-band peak and a defect band or D-bandpeak. For 532 nm excitation, the G-band peak may be at about 1530 toabout 1600 cm⁻¹ and the D-band peak may be at about 1350 to about 1400cm⁻¹. In one example, the D-band peak can be at about 1375 cm⁻¹ to about1380 cm⁻¹ and the G-band peak can be at about 1530 cm⁻¹ to about 1535cm⁻¹ at 532 nm excitation. In another example, the D-band peak can be at1378 cm⁻¹ and the G-band peak can be at 1533 cm⁻¹ at 532 nm excitation.

The parameters of the G-band peak and D-band peak, for example,position, width and intensity ratio, can be used for thecharacterization of the coating layer compound. The G-band may have aG-band magnitude equal to an intensity of the G-band peak (I_(G)) andthe D-band may have a D-band magnitude equal to an intensity of theD-band peak (I_(D)). A ratio of the D-band magnitude to the G-bandmagnitude (I_(D)/I_(G) or D/G) may be determined therefrom, which isequal to the Raman Graphitization Ratio of a material. In some examples,the D/G ratio of the coating layer can be in the range of about 0.5 toabout 0.6, about 0.52 to about 0.58, or about 0.54 to about 0.56.

Deposition of the Coating Layer

Examples of coating methods, for providing a coating layer 30, includechemical vapor deposition (CVD) techniques, and like methods. Specificexamples of CVD techniques include CVD, low pressure CVD, atmosphericpressure CVD, Plasma Enhanced CVD (PECVD), atmospheric plasma CVD,atomic layer deposition (ALD), plasma ALD, and chemical beam epitaxy. Inanother example, the coating layer can be deposited by a pyrolytic torchat temperatures above 600° C., above 800° C., or above 1,000° C.,including any ranges and subranges therebetween.

A gas mixture for forming the coating layer, which contains thehydrocarbon compound, may also comprise a controlled amount of anothercompound, for example, a carrier gas or working gas. The other compoundcan include air, oxygen, nitrous oxide, carbon dioxide, water vapor, orhydrogen peroxide, and/or one or more an inert gas, for example, helium,neon, argon, krypton, xenon.

Surface Energy of the Coating Layer

The coating layer can provide a bonding surface with a surface energy ina range of from about 48 to about 75 mJ/m², as measured for one surface(including polar and dispersion components).

In general, the surface energy of the coating layer can be measured uponbeing deposited and/or after having been further treated, for example byactivation with nitrogen or a mixture of nitrogen and oxygen. Thesurface energy of the as-deposited coating layer prior to any furthersurface activation step, is in the range of about 48 to about 60 mJ/m²,or about 50 to about 58 mJ/m², or equal to or greater than about 50mJ/m², or equal to or less than about 60 mJ/m². After further treatment,for example, the surface energy can be increased to about 75 mJ/m² orless, which provides a good self-propagating bond with a glass sheet,whereby production time to assemble articles is made reasonable and costefficient. Both surface energy ranges (as-deposited—meaning afterdeposition of the layer and without any further treatments applied tothe layer—and after having been further treated) can also be effectiveto control bonding at high temperatures so as to prevent two articlesfrom becoming permanently bonded to one another.

The surface energy of the solid surface is measured indirectly bymeasuring the static contact angles of three liquids—water,diiodomethane and hexadecane—individually deposited on the solid surfacein air. Surface energies as disclosed herein were determined accordingto the Wu model, as set forth below. (See: S. Wu, J. Polym. Sci. C, 34,19, 1971). In the Wu model, the surface energies, including total,polar, and dispersion components, are measured by fitting a theoreticalmodel to three contact angles of three test liquids: water,diiodomethane and hexadecane. From the contact angle values of the threeliquids, a regression analysis is done to calculate the polar anddispersion components of the solid surface energy. The theoretical modelused to calculate the surface energy values includes the following threeindependent equations relating the three contact angle values of thethree liquids and the dispersion and polar components of surfaceenergies of the solid surface (denoted by the subscript “S”) as well asthe three test liquids:

$\begin{matrix}{{\gamma_{W}\left( {1 + {\cos\mspace{14mu}\theta_{W}}} \right)} = {4\left( {\frac{\gamma_{W}^{d}\gamma_{S}^{d}}{\gamma_{W}^{d} + \gamma_{S}^{d}} + \frac{\gamma_{W}^{p}\gamma_{S}^{p}}{\gamma_{W}^{p} + \gamma_{S}^{p}}} \right)}} & (1) \\{{\gamma_{D}\left( {1 + {\cos\mspace{14mu}\theta_{D}}} \right)} = {4\left( {\frac{\gamma_{D}^{d}\gamma_{S}^{d}}{\gamma_{D}^{d} + \gamma_{S}^{d}} + \frac{\gamma_{D}^{p}\gamma_{S}^{p}}{\gamma_{D}^{p} + \gamma_{S}^{p}}} \right)}} & (2) \\{{\gamma_{H}\left( {1 + {\cos\mspace{14mu}\theta_{H}}} \right)} = {4\left( {\frac{\gamma_{H}^{d}\gamma_{S}^{d}}{\gamma_{H}^{d} + \gamma_{S}^{d}} + \frac{\gamma_{H}^{p}\gamma_{S}^{p}}{\gamma_{H}^{p} + \gamma_{S}^{p}}} \right)}} & (3)\end{matrix}$

where, the subscripts “W”, “D” and “H” represent water, diiodomethaneand hexadecane, respectively, and the superscripts “d” and “p” representthe dispersion and polar components of surface energies, respectively.Since diiodomethane and hexadecane are essentially non-polar liquids,the above set of equations reduces to:

$\begin{matrix}{{\gamma_{W}\left( {1 + {\cos\mspace{14mu}\theta_{W}}} \right)} = {4\left( {\frac{\gamma_{W}^{d}\gamma_{S}^{d}}{\gamma_{W}^{d} + \gamma_{S}^{d}} + \frac{\gamma_{W}^{p}\gamma_{S}^{p}}{\gamma_{W}^{p} + \gamma_{S}^{p}}} \right)}} & (4) \\{{\gamma_{D}\left( {1 + {\cos\mspace{14mu}\theta_{D}}} \right)} = {4\left( \frac{\gamma_{D}^{d}\gamma_{S}^{d}}{\gamma_{D}^{d} + \gamma_{S}^{d}} \right)}} & (5) \\{{\gamma_{H}\left( {1 + {\cos\mspace{14mu}\theta_{H}}} \right)} = {4\left( \frac{\gamma_{H}^{d}\gamma_{S}^{d}}{\gamma_{H}^{d} + \gamma_{S}^{d}} \right)}} & (6)\end{matrix}$

From the above set of three equations (4-6), the two unknown parameters,dispersion and polar surface energy components of the solid surface,γ_(S) ^(d) and γ_(S) ^(p), can be calculated by regression analysis.However, with this approach, there is a limiting maximum value up towhich the surface energy of the solid surface could be measured. Thatlimiting maximum value is the surface tension of water, which is about73 mJ/m². If the surface energy of the solid surface is appreciablygreater than the surface tension of water, the surface will be fullywetted by water, thereby causing the contact angle to approach zero.Beyond this value of surface energy, therefore, all calculated surfaceenergy values would correspond to about 73-75 mJ/m² regardless of thereal surface energy value. For example, if the real surface energies oftwo solid surfaces are 75 mJ/m² and 150 mJ/m², the calculated valuesusing the liquid contact angles will be about 75 mJ/m² for bothsurfaces.

Accordingly, all contact angles disclosed herein are measured by placingliquid droplets on the solid surface in air and measuring the anglebetween the solid surface and the liquid-air interface at the contactline. Therefore, when a claim is made on the surface energy value beingfrom 55 mJ/m² to 75 mJ/m² it should be understood that these valuescorrespond to calculated surface energy values based on the methoddescribed above and not the real surface energy values, which could begreater than 75 mJ/m² when the calculated value approaches the realsurface energy value.

Surface Activation of the Coating Layer

The desired surface energy for bonding may not be achieved by thesurface energy of the initially deposited hydrocarbon coating layer.Thus, the deposited coating layer may be optionally further treated. Forexample, after the coating layer 30 is deposited, one or more functionalgroups can optionally be added to add additional bonding capabilities tothe coating layer. For example, adding the functional group can providean additional site of bonding between the coating layer and the secondsheet 20. The functional group can be added using plasma, for exampleatmospheric or low pressure plasma. The functional group is preferablypolar, and can be added using a precursor for example hydrogen, carbondioxide, nitrogen, nitrous oxide, ammonia, acrylic acid, allyl amine,allyl alcohol, or mixtures thereof.

Bonding Energy of the First Sheet or Second Sheet to the Coating Layer

In general, the energy of adhesion (i.e., bond energy) between twosurfaces can be measured by a double cantilever beam method or wedgetest. The tests simulate in a qualitative manner the forces and effectson an adhesive bond join at a coating layer/first sheet or second sheetinterface. Wedge tests are commonly used for measuring bonding energy.For example, ASTM D5041, Standard Test Method for Fracture Strength inCleavage of Adhesives in Bonded Joints, and ASTM D3762, Standard TestMethod for Adhesive-Bonded Surface Durability of Aluminum, are standardtest methods for measuring bonding of substrates with a wedge.

A summary of the test method for determining bond energies as disclosedherein, based on the above-noted ASTM methods, includes recording thetemperature and relative humidity under which the testing is conducted,for example, that in a lab room. The second sheet is gently pre-crackedor separated at a corner of the glass article to break the bond betweenthe first sheet and the second sheet. A razor blade is used to pre-crackthe second sheet from the first sheet, for example, a GEM brand razorwith a thickness of about 228±20 microns. In forming the pre-crack,momentary sustained pressure may be needed to fatigue the bond. A flatrazor having the aluminum tab removed is slowly inserted until the crackfront can be observed to propagate such that the crack and separationincreases. The flat razor does not need to be inserted significantly toinduce a crack. Once a crack is formed, the glass article is permittedto rest for at least 5 minutes to allow the crack to stabilize. Longerrest times may be needed for high humidity environments, for example,above 50% relative humidity.

The glass article with the developed crack is evaluated with amicroscope to record the crack length. The crack length is measured fromthe end separation point of the second sheet from the first sheet (i.e.furthest separation point from the tip of razor) and the closestnon-tapered portion of the razor. The crack length is recorded and usedin the following equation to calculate bond energy.γ=3t _(b) ² E ₁ t _(w1) ³ E ₂ t _(w2) ³/16L ⁴(E ₁ t _(w1) ³ +E ₂ t _(w2)³)  (7)

wherein γ represents the bond energy, t_(b) represents the thickness ofthe blade, razor or wedge, E₁ represents the Young's modulus of thefirst sheet 10 (e.g., a glass carrier), t_(w1) represents the thicknessof the first sheet, E₂ represents the Young's modulus of the secondsheet 20 (e.g., a thin glass sheet), t_(w2) represents the thickness ofthe second sheet 20 and L represents the crack length between the firstsheet 10 and second sheet 20 upon insertion of the razor blade asdescribed above.

The bond energy is understood to behave as in silicon wafer bonding,where an initially hydrogen bonded pair of wafers are heated to convertmuch or all the silanol-silanol hydrogen bonds to Si—O—Si covalentbonds. While the initial, room temperature, hydrogen bonding producesbond energies on the order of about 100-200 mJ/m² which allowsseparation of the bonded surfaces, a fully covalently bonded wafer pairas achieved during processing on the order of 400 to 800° C. has anadhesion energy of about 2000-3000 mJ/m² which does not allow separationof the bonded surfaces; instead, the two wafers act as a monolith. Onthe other hand, if both the surfaces are perfectly coated with a lowsurface energy material, for example a fluoropolymer, with a thicknesslarge enough to shield the effect of the underlying substrate, theadhesion energy would be that of the coating material and would be verylow leading to low or no adhesion between the bonding surfaces.Accordingly, the second sheet 20 (for example a thin glass sheet) wouldnot be able to be processed on first sheet 10 (for example a carrier)without failure of the bond and potential damage to the second sheet 20.Consider two extreme cases: (a) two standard clean 1 (SC1, as known inthe art) cleaned glass surfaces saturated with silanol groups bondedtogether at room temperature via hydrogen bonding (whereby the adhesionenergy is about 100-200 mJ/m²) followed by heating to a temperature thatconverts the silanol groups to covalent Si—O—Si bonds (whereby theadhesion energy becomes 2000-3000 mJ/m²). This latter adhesion energy istoo high for the pair of glass surfaces to be detachable; and (b) twoglass surfaces perfectly coated with a fluoropolymer with low surfaceadhesion energy (about 12-20 mJ/m² per surface) bonded at roomtemperature and heated to high temperature. In this latter case (b), notonly do the surfaces not bond at low temperature (because the totaladhesion energy of about 24-40 mJ/m², when the surfaces are puttogether, is too low), they do not bond at high temperature either asthere are too few polar reacting groups. Between these two extremes, arange of adhesion energies exist, for example between 50-1000 mJ/m²,which can produce the desired degree of controlled bonding. Accordingly,the inventors have found various methods of providing a coating layerleading to a bonding energy between these two extremes, and such thatthere can be produced a controlled bonding sufficient to maintain a pairof sheets (for example a glass carrier and a thin glass sheet) bonded toone another through the rigors of FPD processing but also of a degreethat (even after high temperature processing of, e.g. ≥400° C., ≥500° C.and up to at least 600° C.) allows the detachment of the first sheet(e.g., a carrier) from the second sheet (e.g. a thin sheet) afterprocessing is complete. Moreover, the detachment of the first sheet fromthe second sheet can be performed by mechanical forces, and in such amanner that there is no significant damage to at least the first sheet,and preferably also so that there is no significant damage to the secondsheet.

An appropriate bonding energy can be achieved by using select surfacemodifiers, i.e., coating layer, and/or thermal or nitrogen treatment ofthe surfaces prior to bonding. The appropriate bonding energy may beattained by the choice of chemical modifiers of either one or both ofbonding surface 14 and bonding surface 24, which chemical modifierscontrol both the van der Waal (and/or hydrogen bonding, as these termsare used interchangeably throughout the specification) adhesion energyas well as the likely covalent bonding adhesion energy resulting fromhigh temperature processing (e.g., on the order of ≥400° C., ≥500° C.and up to at least 600° C.).

In some examples, the coating layer can have a bonding surface bonded tothe first or second sheets with bond energy of equal to or less than 700mJ/m², equal to or less than 650 mJ/m², equal to or less 600 mJ/m²,equal to or less 550 mJ/m², or equal to or less than 500 mJ/m²,including any ranges and subranges therebetween, after holding thearticle in a furnace at a temperature of 500° C., 550° C., 600° C. or650° C., including any ranges and subranges therebetween, for 10 minutesin an inert gas (e.g., nitrogen) atmosphere. Bond energy as used hereinis measured after placing an article in a furnace chamber, heating thefurnace at a rate of 9° C. per minute to the test temperature (e.g.,600° C.), holding the article at the test temperature for a period of 10minutes, preferably in an inert atmosphere (e.g., nitrogen), cooling thechamber of the furnace to about 200° C. over a period of time of about 1minute, and then removing the article from the furnace chamber andallowing it to cool to room temperature. This process of testing thearticles can also be referred to as subjecting the articles to a thermaltest cycle.

Production of the Article

In order to produce the article, for example a glass article, thecoating layer 30 is formed on one of the sheets, preferably the firstsheet 10 (for example, a carrier). If desired, the coating layer 30 canbe subjected to steps such as surface activation, and optionally alsoannealing, in order to increase the surface energy, decrease outgassingduring processing and improve the bonding capabilities of the coatinglayer 30, as described herein. In order to bond the other sheet, forexample second sheet 20, the other sheet is brought into contact withthe coating layer 30. If the coating layer 30 has a high enough surfaceenergy, introducing the other sheet to the coating layer 30 will resultin the other sheet being bonded to the coating layer 30 via aself-propagating bond. Self-propagating bonds are advantageous inreducing assembly time and/or cost. However, if a self-propagating bonddoes not result, the other sheet can be bonded to the coating layer 30using additional techniques, such as lamination, for example by pressingthe sheets together with rollers, or by other techniques, as known inthe lamination art for bringing two pieces of material together forbonding.

Outgassing of the Coating Layer

Polymer adhesives used in typical wafer bonding applications aregenerally 10-100 μm thick and lose about 5% of their mass at or neartheir temperature limit. For such materials, evolved from thick polymerfilms, it is easy to quantify the amount of mass loss, or outgassing, bymass-spectrometry. On the other hand, it is more challenging to measurethe outgassing from thin surface treatments that are on the order ofabout 10 to about 100 nm thick or less, for example theplasma-polymerized coating layers described above, as well as for a thinlayer of pyrolyzed silicone oil. For such materials, mass-spectrometryis not sensitive enough. There are a number of other ways to measureoutgassing, however.

TEST #1 of measuring small amounts of outgassing is based on anassembled article, i.e., one in which a thin glass sheet is bonded to aglass carrier via a coating layer to be tested, and uses a change inpercent bubble or bubble area to determine outgassing. During heating ofthe glass article, bubbles formed between the carrier and the thin sheetthat indicate outgassing of the coating layer. The outgassing under thethin sheet may be limited by strong adhesion between the thin sheet andcarrier. Nonetheless, layers ≤10 nm thick (plasma-polymerized materials,for example) may still create bubbles during thermal treatment, despitetheir smaller absolute mass loss. And the creation of bubbles betweenthe thin sheet and carrier may cause problems with pattern generation,photolithography processing, and/or alignment during device processingonto the thin sheet. Additionally, bubbling at the boundary of thebonded area between the thin sheet and the carrier may cause problemswith process fluids from one process entering a bubble in that oneprocess, and leaving the bubble in a downstream process thuscontaminating that downstream process. A change in percent bubble areaof ≥10 or ≥5 is significant, indicative of outgassing, and is notdesirable. On the other hand a change in percent bubble area of ≤3 or ≤1is insignificant and an indication that there has been no outgassing.

The average bubble area of bonded glass sheets in a class 1000 cleanroom with manual bonding is about 1%. The percent of bubbles in bondedsheets is a function of cleanliness of the first sheet, the secondsheet, and surface preparation. Because these initial defects act asnucleation sites for bubble growth after heat treatment, any change inbubble area upon heat treatment less than about 1% is within thevariability of sample preparation. To carry out this test, acommercially available desktop scanner with transparency unit (EpsonExpression 10000XL Photo) was used to make a first scan image of thearea bonding the first sheet and the second sheet immediately afterbonding. The articles were scanned using the standard Epson softwareusing 508 dpi (50 μm/pixel) and 24 bit RGB. The image processingsoftware first prepares an image by stitching, as necessary, images ofdifferent sections of a sample into a single image and removing scannerartifacts (by using a calibration reference scan performed without asample in the scanner). The bonded area is then analyzed using standardimage processing techniques, for example thresholding, hole filling,erosion/dilation, and blob analysis. The Epson Expression 11000XL Photomay also be used in a similar manner. In transmission mode, bubbles inthe bonding area are visible in the scanned image and a value for bubblearea can be determined. Then, the bubble area is compared to the totalbonding area (i.e., the total overlap area between the thin sheet andthe carrier) to calculate a percent area of the bubbles in the bondingarea relative to the total bonding area. The samples are then heattreated in a MPT-RTP600s Rapid Thermal Processing system, available fromModular Process Technology (MPT, with offices in San Jose, Calif.) underN₂ atmosphere at test-limit temperatures of 300° C., 400° C., 500° C.and 600° C., for up to 10 minutes. Specifically, the time-temperaturecycle carried out included: inserting the article into the heatingchamber at room temperature and atmospheric pressure; the chamber wasthen heated to the test-limit temperature at a rate of 9° C. per minute;the chamber was held at the test-limit temperature for 10 minutes; thechamber was then cooled at furnace rate over about 1 minute to about200° C.; the article was removed from the chamber and allowed to cool toroom temperature; the article was then scanned a second time with theoptical scanner. The percent bubble area from the second scan was thencalculated as above and compared with the percent bubble area from thefirst scan to determine a change in percent bubble area. As noted above,a change in bubble area of ≥10% is significant and an indication ofoutgassing. A change in percent bubble area was selected as themeasurement criterion because of the variability in original percentbubble area. That is, most coating layers have a bubble area of about 2%in the first scan due to handling and cleanliness after the thin sheetand carrier have been prepared and before they are bonded. However,variations may occur between materials.

The percent bubble area measured, as exemplified by the change inpercent bubble area, can also be characterized as the percent of totalsurface area of the coating layer bonding surface not in contact withthe first sheet bonding surface. As described above, the percent oftotal surface area of the coating layer bonding surface not in contactwith the first sheet is desirably less than 10%, less than 5%, less than3%, less than 1% and up to less than 0.5% after the glass article issubjected to a temperature cycle by heating in a chamber cycled fromroom temperature to 500° C., 600° C., 650° C., and up to 700° C.,including any ranges and subranges therebetween, at a rate 9° C. perminute and then held at the test temperature for 10 minutes beforecooling the chamber to about 200° C. in about 1 minute and removing thearticle from the chamber and allowing the glass article to cool to roomtemperature. The coating layer described herein allows the first sheetto be separated from the second sheet without breaking the first sheetinto two or more pieces after the glass article is subjected to theabove temperature cycling and thermal testing.

Processing of the Glass Article

The use of a coating layer, together with bonding surface preparation asappropriate, can achieve a controlled bonding area, that is, a bondingarea capable of providing a room-temperature bond between the firstsheet and the second sheet sufficient to allow the article to beprocessed in FPD type processes (including vacuum and wet processes),and yet one that controls covalent bonding between the first sheet andthe second sheet (even at elevated temperatures) so as to allow thefirst sheet to be removed from the second sheet (without damage to thesheets) after high temperature processing of the article, for example,FPD type processing or LTPS processing. To evaluate potential bondingsurface preparations and coating layers with various bonding energiesthat would provide a reusable carrier suitable for FPD processing, aseries of tests were used to evaluate the suitability of each. DifferentFPD applications have different requirements, but LTPS and Oxide TFTprocesses appear to be the most stringent at this time. Thus, testsrepresentative of steps in these processes were chosen, as these aredesired applications for the article 2. Annealing at 400° C. is used inoxide TFT processes, whereas crystallization and dopant activation stepsover 600° C. are used in LTPS processing. Accordingly, the followingtesting was carried out to evaluate the likelihood that a particularbonding surface preparation and the coating layer would allow a thinsheet to remain bonded to a carrier throughout FPD processing, whileallowing the thin sheet to be removed from the carrier (without damagingthe thin sheet and/or the carrier) after such processing (includingprocessing at temperatures ≥400° C. and up to less than 700° C.).

EXAMPLES Example 1

A methane precursor compound was deposited as coating layers on Corning®EAGLE XG® alkali-free display glass having a thickness of about 0.7 mm.Methane at about 1 weight percent of a carrier gas of helium at a rateof 50 to 100 sccm and at room temperature was deposited with a Linearatmospheric pressure plasma head at a power in the range of 400 to 750Watts and a frequency of 13.56 MHz. A scan speed in the range of 20 to60 mm per seconds was used to deposit the coating layers and the plasmahead was placed away from the display glass at a distance in the rangeof 10 to 30 mm. The coated carriers were then bonded to clean 100 μmthin glass sheets (made of Corning® Willow® glass). Prior to bonding,the Willow® glass was cleaned in a typical display clean line in 2%Semiclean KG at 65° C. and well rinsed, and cleaned in dilute SC1(40:1:2 DI:JTB111: H₂O₂ (30%) 65° C./10 min.), and spin rinse dried.

FIG. 3 shows the bond energy (mJ/m², left-hand Y-axis, filled diamonddata points) and outgassing (change in percent bubble area, right-handY-axis, filled square data points) of a first glass article including afirst methane-based coating layer deposited at 25° C. with a thicknessof less than about 3 nm (1 scan), and of a second glass articleincluding a second methane-based coating layer deposited at 25° C. witha thickness of less than about 5 nm (2 scan), and both the first andsecond glass articles including a thin glass sheet (thickness of 100microns) coupled to the carrier via the respective coating layer. Asdeposited, the first and second methane-based coating layers produced abond energy between the thin glass sheet and the carrier of about 577mJ/m² and 439 mJ/m², respectively, after holding the glass article in afurnace at a temperature of 600° C. for 10 minutes in a nitrogenatmosphere. Bond energy was measured by a wedge insertion method asdescribed above. As deposited, the first and second methane-basedcoating layers exhibited a change in bubble area of about 2.45% andabout 2.95%, respectively, after holding the glass article in a furnaceat a temperature of 600° C. for 10 minutes in a nitrogen atmosphere,which is consistent with minimal to no outgassing. Bubble area wasdetermined using TEST #1. As can be seen, as the bond energy decreases,the bubble area increases, indicating that the percent of the surface ofthe thin glass sheet bonded to the coating layer is decreasing. However,the bubble area is below 5% and this material is useful up to atemperature of at least about 600° C.

The as-deposited measured surface energy was 51.94 mJ/m² for the 1-scancoating and 44.81 mJ/m² for the 2-scan coating.

FIG. 7 shows a comparison of surface energy over a range of coatinglayer thicknesses for coating layers by depositing methane as disclosedin WO 2015/112958, wherein the surface energies were well below 49 mJ/m²and decreased significantly as thickness increased.

Optical band gap for the coating layers of Example 1 were measured asabout 1.53 eV.

Comparative Example 2

A methane precursor compound was deposited as a coating layer onCorning® EAGLE XG® alkali-free display glass having a thickness of about0.7 mm. The coating layer was deposited in a Plasmatherm HDPCVDapparatus using a gas source of 20 standard cubic centimeters per minute(sccm) of C₂H₄ and 40 sccm of H₂. The coating was deposited for a periodof 180 seconds at a chamber pressure of 5 mT, a power of 1500 W and afrequency of 2 kHz applied to the coil, and a frequency of 13.56 MHzapplied to the platen.

Coating layers were characterized by contact angle measurements with aKruss goniometer (available from Kruss GmbH, Hamburg Germany) usingwater, hexadecane, and diiodomethane fluids and fit using the Wu model.A Wollam spectroscopic ellipsometer (available from J. A. Wollam Co.,Lincoln, Nebr.) was used to measure coating layer thickness. Themeasured thickness of the as-deposited coating was about 782 Angstroms(about 78.2 nm). The as-deposited measured surface energy was 46.7 mJ/m²for the coating. The measured surface energy was well below the 51.94mJ/m² surface energy of the 1-scan coating of Example 1. Optical bandgap for the coating layer was measured as about 3.27 eV. The measuredoptical band gap was well above the 1.53 eV optical band gap of thecoatings of Example 1.

Example 3

Plasma-polymerized ethylene coating layers were deposited on 0.7 mmthick EAGLE XG® carriers with a Nextral NE5000 parallel plate reactiveion etch (RIE) machine available from Corial, having headquarters inBemin, France) using ethylene and hydrogen gas sources. Depositionconditions were a chamber pressure of 30 mT, a power of 500 W, 8standard cubic centimeters per minute (sccm) of C₂H₄ and 92 sccm of H₂,and a platen temperature of 40° C. The as-deposited coating layers werethen surface activated with a nitrogen and oxygen mixture of 25 sccm N₂25 sccm O₂ 10 mT 500 W. The coated carriers were then bonded to clean100 μm thin glass sheets (made of Corning® Willow® glass). Prior tobonding, the Willow® glass was cleaned in a typical display clean linein 2% Semiclean KG at 65° C. and well rinsed, and cleaned in dilute SC1(40:1:2 DI:JTB111: H₂O₂ (30%) 65° C./10 min.), and spin rinse dried.

Coating layers were characterized by contact angle measurements with aKruss goniometer (available from Kruss GmbH, Hamburg Germany) usingwater, hexadecane, and diiodomethane fluids and fit using the Wu model.A Wollam spectroscopic ellipsometer (available from J. A. Wollam Co.,Lincoln, Nebr.) was used to measure coating layer thickness, roughnessand dispersion using a Tauc Lorentz model. Index and thickness were alsomeasured with an n&k analyzer using a single F-K oscillator modelincluded with the accompanying software. Bond energy was measured by thewedge insertion method described above.

FIG. 4 shows the change in surface energy of the coating layer prior tobonding with the thin glass and during activation with the nitrogen andoxygen mixture. In this figure, filled diamond data points are thicknessin angstroms (“A”) according to the scale on the left-hand Y-axis, andthe filled square data points are surface energy in mJ/m² according tothe scale on the right-hand Y-axis. The as-deposited thickness of thecoating layer was about 103 Angstrom (about 10.3 nm) and theas-deposited surface energy (at time equals 0) was about 54 mJ/m².Activation with nitrogen and oxygen for 5 seconds (“s”) increased thesurface energy to about 72 mJ/m² and the thickness decreased to about 97Angstroms (about 9.7 nm). Accordingly, longer N₂—O₂ exposure times leadto decreased thickness and increased surface energy.

FIG. 5 shows the bond energy (mJ/m², left-hand Y-axis, filled diamonddata points) and outgassing (change in percent bubble area, right-handY-axis, filled square data points) of a glass articles includingethylene-based coating layers of having thicknesses of about 37Angstroms (about 3.7 nm), about 44 Angstroms (about 4.4 nm) and about 46Angstroms (about 4.6 nm). The glass articles were held in a furnace at500° C. for 10 minutes in a nitrogen atmosphere. The furnace was heatedat a rate of 9° C. per minute to the 500° C. test temperature and after10 minutes at the test temperature the furnace was cooled to about 200°C. in about 1 minute, and then the glass article was removed and allowedto cool to room temperature. The coating layers produced a bond energyof about 500 mJ/m² at a layer thickness of about 3.7 nm, about 325 mJ/m²at a layer thickness of about 4.4 nm and about 275 mJ/m² at a layerthickness of about 4.6 nm. The coating layers exhibited a bubble areachange of about 0% at a layer thickness of about 3.7 nm, about 1% at alayer thickness of about 4.4 nm and about 8.5% at a layer thickness ofabout 4.6 nm; wherein all of these changes in percent bubble area areconsistent with no outgassing. Coating layers having a thickness in therange of about 3.5 nm to about 4.5 nm provided an advantageouscombination of bonding energy (high enough to allow the articles to beprocessed in display making processes without coming apart and yet lowenough after the desired heat treatment to allow the sheets to separatewithout breaking) and low outgassing (as measured by bubble area change)to avoid process contamination.

FIG. 6 shows the bond energy (mJ/m², left-hand Y-axis, filled diamonddata points) and outgassing (change in percent bubble area, right-handY-axis, filled square data points) of glass articles includingethylene-based coating layers over a range of temperatures. The glassarticles were held at each specified temperature for 10 minutes in anitrogen atmosphere and the coating layers had a thickness of about 44Angstroms (about 4.4 nm). The coating layers produced a bond energy ofabout 250 mJ/m² at a temperature of about 25° C. (room temperature),about 400 mJ/m² after a thermal test cycle to a temperature of about300° C., about 515 mJ/m² after a thermal test cycle to a temperature ofabout 400° C., about 270 mJ/m² after a thermal test cycle to atemperature of about 500° C., and about 320 mJ/m² after a thermal testcycle to a temperature of about 600° C.; all of these bond energies arewithin the range allowing the sheets to be separated without damage. Thecoating layers exhibited a bubble area change of about 0% at atemperature of about 25° C., about 0% at a temperature of about 300° C.,about 0% at a temperature of about 400° C., about 8.5% at a temperatureof about 500° C., and about 7.5% at a temperature of about 600° C.wherein all of these changes in percent bubble area are consistent withno outgassing.

FIG. 8 shows a graph of Raman characterization of a hydrogenatedamorphous plasma-polymerized hydrocarbon coating layer formed by anethylene precursor of this Example. The coating layer compositionexhibits a D-band peak at 1378 cm⁻¹ and a G-band peak at 1533 cm⁻¹ at532 nm excitation and demonstrates that the coating is a hydrogenatedamorphous carbon material. The I_(D)/I_(G) ratio for the coating layeris 0.55, which is indicative of a diamond-like carbon (DLC) film.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the examples disclosedherein without departing from the spirit and scope of the claimedsubject matter. Many variations and modifications may be made to theabove-described examples without departing substantially from the spiritand various principles described. All such modifications and variationsare intended to be included herein within the scope of this disclosureand protected by the following claims.

What is claimed is:
 1. An article comprising: a first sheet comprising afirst sheet bonding surface; and a coating layer comprising a firstcoating layer bonding surface and a second coating layer bondingsurface, the coating layer comprising a polymerized hydrogenatedamorphous hydrocarbon compound, the coating layer comprising anintensity ratio (D/G ratio) of a peak (D band) appearing in a range of1350 to 1400 cm·1 to a peak (G band) appearing in a range of 1530 to1600 cm·1 of a Raman spectrum of the coating layer in a range of about0.5 to about 0.6, and at least one of the following: a refractive indexabove about 1.8; an optical band gap of less than 2 eV.
 2. The articleof claim 1, further comprising a second sheet comprising a second sheetbonding surface, wherein the second coating layer bonding surface isbonded with the second sheet bonding surface.
 3. The article of claim 2,wherein the first sheet is a glass sheet and/or the second sheet is aglass sheet.
 4. The article of claim 1, wherein the coating layer has anaverage thickness of less than about 10 nm and is optionally is a singlelayer.
 5. The article of claim 1, the first sheet having an averagethickness less than about 200 μm.
 6. The article of claim 1, wherein thefirst coating layer bonding surface is bonded with the first sheetbonding surface with a bond energy of equal to or less than 600 mJ/m2after holding the article in a furnace at a temperature of 600° C. for10 minutes in a nitrogen atmosphere.
 7. The article of claim 1, thechange in percent bubble area of the coating layer being less than orequal to about 10 percent according to Outgassing Test #1 after holdingthe article in a furnace at a temperature of 600° C. for 10 minutes in anitrogen atmosphere.
 8. The article of claim 1, the change in percentbubble area of the coating layer being less than 10 percent according toOutgassing Test #1 after holding the article in a furnace at atemperature of 500° C. for 10 minutes in a nitrogen atmosphere.
 9. Thearticle of claim 1, wherein the coating layer has an average thicknessof less than 5 nm.